1. Field of the Invention
The present invention relates generally to optical waveguides, and more specifically to microstructured optical waveguides having large optical nonlinearity.
2. Technical Background
Optical waveguides are used in optical applications where the optical nonlinearity of the waveguide provides a desired effect. For example, silica-based optical waveguide fibers are used to convey soliton pulses in the fiber based in part on the optical nonlinear effect of self-phase modulation. As another example, silica-based fibers are used in signal amplification or signal modification applications, such as parametric amplification, where the amplification depends on the optical nonlinearity of the fiber material.
In general, the polarization response of a material to an electric field due to light will have both a linear and a non-linear component. The linear component of the polarization response linearly increases with the electric field of the light. The non-linear component increases with higher order electric field terms, i.e., greater than the first power of the electric field.
For many applications, the third order component provides the most significant contribution to the nonlinearity of the fiber, and the nonlinearity may be approximately expressed in terms of the third order component alone. In such a case, the non-linear polarization PNL can be expressed as: PNL="khgr"(3)xc3x97(third order Electric field terms). Thus, "khgr"(3) is often used as a measure of the optical nonlinearity of a material.
Alternatively, optical nonlinearity may be expressed in terms of the change in refractive index due to the light intensity (which is proportional to the square of the electric field). The refractive index can be expressed as: n=no+xcex94n, where no is the constant portion of the refractive index dependent only upon the frequency of the light, and xcex94n is the refractive index change which is dependent on both frequency and intensity. At a given wavelength, the refractive index change xcex94n can be expressed as: xcex94n=xcex3I, where I is the intensity of the light. Thus, xcex3 is an alternative expression for the nonlinearity of a material. For many materials, "khgr"(3) and xcex3 are related by the equation: "khgr"(3)≅6.3xc3x97n2xc3x97xcex3, where "khgr"(3) and xcex3 are measured in esu units.
Silica-based optical waveguide fibers are often used for optical applications that depend on the optical nonlinearity of the fiber material. Silica, however, is not a strongly nonlinear material. Thus, achieving the desired non-linear effects requires the implementation of undesirable compensation techniques, such as using higher intensity light or longer fiber lengths.
One aspect of the present invention relates to a microstructured optical waveguide, the optical waveguide supporting the propagation of an optical signal of a desired wavelength. The optical waveguide includes a core region and a cladding region. The core region is formed from an optically nonlinear material having a xcex3 of at least about 2.5xc3x9710xe2x88x9219 m2/W at 1260 nm. The cladding region surrounds the core region and includes a bulk material and a plurality of columns arranged in the bulk material, each column having a cross-sectional area. The number, arrangement, and areas of the columns are selected such that the dispersion of the optical signal at the desired wavelength is within the range of about xe2x88x9270 ps/nm-km to about 70 ps/nm-km.
Another aspect of the present invention relates to a microstructured optical fiber, the optical fiber supporting the propagation of an optical signal of a desired wavelength. The optical fiber includes a core region and a cladding region. The core region is formed from an optically nonlinear material having a xcex3 of at least about 2.5xc3x9710xe2x88x9219 m2/W at 1260 xcexcm. The cladding region surrounds the core region and includes a bulk material and a plurality of columns arranged in the bulk material, each column having a cross-sectional area. The number, arrangement, and areas of the columns are selected such that the dispersion of the optical signal at the desired wavelength is within the range of about xe2x88x9270 ps/nm-km to about 70 ps/nm-km.
Another aspect of the present invention relates to an optical communication system for the propagation of an optical signal. The optical communication system comprises a microstructured optical waveguide, the optical waveguide supporting the propagation of an optical signal of a desired wavelength, a signal radiation source for providing the signal at the desired wavelength, and a signal coupler for coupling the signal into the optical waveguide. The optical waveguide includes a core region and a cladding region. The core region is formed from an optically nonlinear material having a xcex3 of at least about 2.5xc3x9710xe2x88x9219 m2/W at 1260 nm. The cladding region surrounds the core region and includes a bulk material and a plurality of columns arranged in the bulk material, each column having a cross-sectional area. The number, arrangement, and areas of the columns are selected such that the dispersion of the optical signal at the desired wavelength is within the range of about xe2x88x9270 ps/nm-km to about 70 ps/nm-km.
The waveguides and communications systems of the present invention result in a number of advantages over prior art waveguides and communications systems. For example, nonlinear phenomena at communications wavelengths can be exploited in the waveguides of the present invention at much lower powers than in conventional waveguides. Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from the description or recognized by practicing the invention as described in the written description and claims hereof, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework to understanding the nature and character of the invention as it is claimed.
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.